Lipoic acid derivatives

ABSTRACT

Lipoic acid derivatives and pharmaceutical formulations containing lipoic acid derivatives are useful in the treatment and prevention of disease characterized by disease cells that are sensitive to lipoic acid derivatives.

RELATED APPLICATIONS

This application is a continuation patent application of U.S. patentapplication Ser. No. 12/105,096, filed Apr. 17, 2008, which claims thebenefit of and priority to U.S. provisional patent application Ser. No.60/912,598, filed Apr. 18, 2007; the contents of each of which arehereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention is directed to lipoic acid derivatives or saltsthereof which selectively kill tumor cells by altering cancer cellmetabolism and signal transduction pathways linked to the WarburgEffect, as well as to methods of treating a subject with such lipoicacid derivatives.

2. Related Background Art

All mammalian cells require energy to live and grow. Cells obtain thisenergy by metabolizing food molecules by oxidative metabolism. The vastmajority of normal cells utilize a single metabolic pathway tometabolize their food. The first step in this metabolic pathway is thepartial degradation of glucose molecules to pyruvate in a process knownas glycolysis which yields two ATP units. Glycolysis can occur evenunder hypoxic conditions. Pyruvate is further degraded in themitochondrion by a process known as the tricarboxylic acid (TCA) cycleto produce thirty-six ATP units per glucose molecule, water and carbondioxide. The TCA cycle requires oxygen. During periods of reduced oxygenlevels, normal cells adapt by a variety of mechanisms and return tonormal metabolism as oxygen levels are restored. A critical link betweenglycolysis and the TCA cycle is an enzyme known as pyruvatedehydrogenase (“PDH”). PDH is part of a larger multi-subunit complex(hereinafter “PDC”). PDH, in conjunction with other enzymes of the PDCcomplex, produces acetyl CoA which effectively funnelsglycolysis-produced pyruvate to the TCA cycle.

Most cancers display profound perturbation of energy metabolism. One ofthe fundamental changes is the adoption of the Warburg Effect, whereglycolysis becomes the main source of ATP. An ATP deficit followsreduced TCA ATP generation. In other words, cancer cells behave as ifthey are hypoxic even when they are not. This change in energymetabolism represents one of the most robust and well-documentedcorrelates of malignant transformation and has been linked to otherchanges resulting in tumor growth and metastasis. Because of the reducedlevels of ATP available as a result of glycolysis largely beingde-linked from the TCA cycle, cancer cells increase their uptake ofglucose and its conversion to pyruvate in an attempt to make up theenergy deficit. Excess pyruvate and other metabolic by-products of theWarburg biochemistry must be managed. A number of these metabolites areknown to be cytotoxic, e.g., acetaldehyde. PDC in cancer along withother related enzymes plays a major role in managing and/or detoxifyingthe excess pyruvate and metabolites. For example, the joining of twoacetyl molecules to form the neutral compound acetoin. This generationof acetoin is catalyzed by a tumor-specific form of PDC.

It has been suggested that lipoic acid acts as a cofactor with PDC andrelated lipoamide using enzymes in detoxifying these otherwise toxicmetabolites. Whether lipoic acid is made by healthy and cancer cells orwhether it is an essential nutrient is debated in the literature, andboth may be the case. The genes required to produce lipoic acid havebeen identified in mammalian cells. Whether mitochondrial pumps oruptake mechanisms are present in healthy or cancer cells or whether theydiffer in diverse tissues is not known. Although the TCA cycle stillfunctions in cancer cells, the tumor cell TCA cycle is a variant cyclewhich depends on glutamine as the primary energy source. Inhibition orinactivation of tumor-specific PDC and related enzymes that detoxifymetabolites may promote apoptosis or necrosis and cell death.

Despite extensive work characterizing the highly conserved changes amongdiverse tumor types and their metabolism, the changes remain to besuccessfully exploited as a target for cancer chemotherapy. As cancerremains the number two killer of Americans, there is an urgent need fornew approaches to disease management. It has been suggested that lipoicacid due to its redox potential properties may be useful in thetreatment of diverse diseases involving mitochondrial function such asdiabetes, Alzheimers disease and cancer. These reports teach that theavailability of the redox shift from SH to S—S be maintained to have thedesired effect.

U.S. Pat. Nos. 6,331,559 and 6,951,887 disclose a novel class oftherapeutic agents which selectively targets and kills tumor cells andcertain other types of diseased cells. These patents further disclosepharmaceutical compositions comprising an effective amount of a lipoicacid derivative according to its invention along with a pharmaceuticallyacceptable carrier. The present inventors have now discovered additionallipoic acid derivatives beyond the scope of the aforementioned patents.

SUMMARY OF THE INVENTION

In a first aspect, the present invention is directed to a lipoic acidderivative having formula (I):

wherein R₁ and R₂ are independently selected from the group consistingof acyl defined as R₃C(O), heteroaryl, imidoyl defined as R₄C(═NH)—,organometallic aryl, and alkyl-organometallic aryl; wherein R₁ and R₂ asdefined above can be unsubstituted or substituted; wherein R₃ isselected from the group consisting of hydrogen, alkenyl, alkynyl,alkylaryl, heteroaryl, alkylheteroaryl and organometallic aryl, any ofwhich can be substituted or unsubstituted; wherein R₄ is selected fromthe group consisting of hydrogen, alkenyl, alkynyl, aryl, alkylaryl,heteroaryl, and alkylheteroaryl, any of which can be substituted orunsubstituted; and wherein x is 0-16; or a salt thereof.

The present invention is further directed to a lipoic acid derivativehaving formula (I), wherein R₁ and R₂ are independently selected fromthe group consisting of acyl defined as R₃C(O), alkyl defined asC_(n)H_(2n+1), alkenyl defined as C_(m)H_(2m−1), alkynyl defined asC_(m)H_(2m−3), aryl, heteroaryl, alkyl sulfide defined asCH₃(CH₂)_(n)—S—, imidoyl defined as R₄C(═NH)—, and hemiacetal defined asR₅CH(OH)—S—; wherein R₁ and R₂ as defined above can be unsubstituted orsubstituted; wherein R₃ and R₄ are independently selected from the groupconsisting of hydrogen, alkyl, alkenyl, alkynyl, cycloalkyl, aryl,alkylaryl, heteroaryl, and heterocyclyl, any of which can be substitutedor unsubstituted; wherein R₅ is selected from the group consisting ofCCl₃, CF₃ and COOH; and wherein x is 0-16, n is 0-10 and m is 2-10;provided that at least one of R₁ and R₂ is independently selected fromthe group consisting of acyl defined as R₃C(O), heteroaryl, imidoyldefined as R₄C(═NH)—, organometallic aryl, and alkyl-organometallicaryl, with R₃ being selected from the group consisting of hydrogen,alkenyl, alkynyl, alkylaryl, heteroaryl, alkylheteroaryl organometallicaryl, and alkyl-organometallic aryl, any of which can be substituted orunsubstituted, and R₄ being selected from the group consisting ofhydrogen, alkenyl, alkynyl, aryl, alkylaryl, heteroaryl, andalkylheteroaryl, any of which can be substituted or unsubstituted; or asalt thereof.

Another embodiment of the invention, is directed to a lipoic acidderivative having formula (I), wherein R₁ and R₂ are independentlyselected from the group consisting of acyl defined as R₃C(O), alkyldefined as C_(n)H_(2n+1), alkenyl defined as C_(m)H_(2m−1), alkynyldefined as C_(m)H_(2m−3), aryl, heteroaryl, alkyl sulfide defined asCH₃(CH₂)_(n)—S—, imidoyl defined as R₄C(═NH)—, hemiacetal defined asR₅CH(OH)—S—, and hydrogen provided that at least one of R₁ and R₂ ishydrogen; wherein R₁ and R₂ as defined above can be unsubstituted orsubstituted; wherein R₃ is independently selected from the groupconsisting of hydrogen, alkenyl, alkynyl, cycloalkyl, aryl, alkylaryl,heteroaryl, alkylheteroaryl and heterocyclyl, any of which can besubstituted or unsubstituted; wherein R₄ is independently selected fromthe group consisting of hydrogen, alkyl, alkenyl, alkynyl, cycloalkyl,aryl, alkylaryl, heteroaryl, and heterocyclyl, any of which can besubstituted or unsubstituted; wherein R₅ is selected from the groupconsisting of CCl₃, CF₃ and COOH; and wherein x is 0-16, n is 0-10 and mis 2-10; or a salt thereof.

The invention is further directed to a lipoic acid derivative havingformula (I), wherein R₁ and R₂ are independently selected from the groupconsisting of alkyl sulfide defined as CH₃(CH₂)_(n)—S— and hemiacetaldefined as R₅CH(OH)—S—; wherein R₁ and R₂ as defined above can beunsubstituted or Substituted and wherein at least one of R₁ and R₂ issubstituted; wherein R₅ is selected from the group consisting of CCl₃,CF₃ and COOH; and wherein x is 0-16, n is 0-10 and m is 2-10; or a saltthereof.

A further embodiment of the invention is directed to a lipoic acidderivative having formula (I), wherein R₁ and R₂ are independentlyselected from the group consisting of acyl defined as R₃C(O), alkyldefined as C_(n)H_(2n+1), alkenyl defined as C_(m)H_(2m−3), alkynyldefined as C_(m)H_(2m−3), aryl, heteroaryl, alkyl sulfide defined asCH₃(CH₂)_(n)—S—, imidoyl defined as R₄C(═NH)—, and hemiacetal defined asR₅CH(OH)—S—; wherein R₁ and R₂ as defined above can be unsubstituted orsubstituted; wherein R₃ and R₄ are independently selected from the groupconsisting of hydrogen, alkyl, alkenyl, alkynyl, cycloalkyl, aryl,alkylaryl, heteroaryl, and heterocyclyl, any of which can be substitutedor unsubstituted; wherein R₅ is selected from the group consisting ofCCl₃, CF₃ and COOH; and wherein x is 0-16, n is 0-10 and m is 2-10;provided that at least one of R₁ and R₂ is independently selected frontthe group consisting of an alkyl sulfide defined as CH₃(CH₂)_(n)—S— andhemiacetal defined as R₅CH(OH)—S—, said at least one of R₁ and R₂ beingsubstituted; or a salt thereof.

The present invention is still further directed to a lipoic acidderivative having formula (II):

wherein M is —[C(R₁)(R₂)]_(z); wherein R₁ and R₂ are independentlyselected from the group consisting of acyl defined as R₃C(O)—, alkyldefined as C_(n)H_(2n+1), alkenyl defined as C_(m)H_(2m−1), alkynyldefined as C_(m)H_(2m−3), aryl, heteroaryl, alkyl sulfide defined asCH₃(CH₂)_(n)—S—, imidoyl defined as R₃C(═NH)—, hemiacetal defined asR₄CH(OH)—S— and hydrogen; wherein R₁ and R₂ as defined above can beunsubstituted or substituted; wherein R₃ and R₄ are independentlyselected from the group consisting of hydrogen, alkyl, alkenyl, alkynyl,cycloalkyl, aryl, alkylaryl, heteroaryl, and heterocyclyl, any of whichcan be substituted or unsubstituted; wherein R₅ is selected from thegroup consisting of CCl₃, CF₃ or COOH; and wherein x is 0-16, z is 0-5,n is 0-10 and m is 2-10; or a salt thereof.

Further embodiments of the present invention include those havingformula (I) in which one or both of the R₁ and R₂ groups include analkylaryl substituent, an alkyl substituent, with a heteroatom in thecarbon chain, a substituted acyl group or a substituted alkyl group.

A still further embodiment of the present invention is directed to apharmaceutical formulation comprising (a) a therapeutically effectiveamount of at least one lipoic acid derivative of any of the embodimentsof the invention and (b) at least one pharmaceutically acceptableadditive. In preferred embodiments, the at least one pharmaceuticallyacceptable additive is selected from solvents, diluents, surfactants,solubilizers, preservatives, buffers, and combinations thereof and/orthe at least one lipoic acid derivative is present in an amount toprovide from about 0.001 mg/m² to about 10 g/m².

Still further embodiments of the invention are directed to methods oftreating or preventing a disease characterized by disease cells that aresensitive to lipoic acid derivatives comprising administering to apatient in need thereof a therapeutically effective amount of at leastone lipoic acid derivative according to any of the embodiments of theinvention. In preferred embodiments, the at least one lipoic acidderivative is in a pharmaceutical formulation further comprising atleast one pharmaceutically acceptable additive.

DETAILED DESCRIPTION

The present invention is directed to lipoic acid derivatives which areeffective to target and kill tumor cells. Accordingly, in a firstembodiment, the present invention is directed to a lipoic acidderivative having formula (I):

wherein R₁ and R₂ are independently selected from the group consistingof acyl defined as R₃C(O), heteroaryl, imidoyl defined as R₄C(═NH)—,organometallic aryl, and alkyl-organometallic aryl;

wherein R₁ and R₂ as defined above can be unsubstituted or substituted;

wherein R₃ is selected from the group consisting of hydrogen, alkenyl,alkynyl, alkylaryl, heteroaryl, alkylheteroaryl and organometallic aryl,any of which can be substituted or unsubstituted;

wherein R₄ is selected from the group consisting of hydrogen, alkenyl,alkynyl, aryl, alkylaryl, heteroaryl, and alkylheteroaryl, any of whichcan be substituted or unsubstituted; and

wherein x is 0-16;

or a salt thereof.

In a second embodiment, the present invention is directed to a lipoicacid derivative having formula (I):

wherein R₁ and R₂ are independently selected from the group consistingof acyl defined as R₃C(O), alkyl defined as C_(n)H_(2n+1), alkenyldefined as C_(m)H_(2m−1), alkynyl defined as C_(m)H_(2m−3), aryl,heteroaryl, alkyl sulfide defined as CH₃(CH₂)_(n)—S—, imidoyl defined asR₄C(═NH)—, and hemiacetal defined as R₅CH(OH)—S—;

wherein R₁ and R₂ as defined above can be unsubstituted or substituted;

wherein R₃ and R₄ are independently selected from the group consistingof hydrogen, alkyl, alkenyl, alkynyl, cycloalkyl, aryl, alkylaryl,heteroaryl, and heterocyclyl, any of which can be substituted orunsubstituted;

wherein R₅ is selected from the group consisting of CCl₃, CF₃ and COOH;and

wherein x is 0-16, n is 0-1.0 and m is 2-10;

provided drat at least one of R₁ and R₂ is independently selected fromthe group consisting of acyl defined as R₃C(O), heteroaryl, imidoyldefined as R₄C(═NH)—, organometallic aryl, and alkyl-organometallicaryl, with R₃ being selected from the group consisting of hydrogen,alkenyl alkynyl, alkylaryl, heteroaryl, alkylheteroaryl, organometallicaryl, and alkyl-organometallic aryl, any of which can be substituted orunsubstituted, and R₄ being selected from the group consisting ofhydrogen, alkenyl, alkynyl, aryl, alkylaryl heteroaryl andalkylheteroaryl, any of which can be substituted or unsubstituted;

or a salt thereof.

Particularly preferred lipoic acid derivatives of the first and secondembodiments include:

In a third embodiment, the present invention is directed to a lipoicacid derivative having formula (I):

wherein R₁ and R₂ are independently selected from the group consisting:of acyl defined as R₃C(O), alkyl defined as C_(n)H_(2n+1), alkenyldefined as C_(m)H_(2m−1), alkynyl defined as C_(m)H_(2m−3), aryl,heteroaryl, alkyl sulfide defined as CH₃(CH₂)_(n)—S—, imidoyl defined asR₄C(═NH)—, hemiacetal defined as R₅CH(OH)—S—, and hydrogen provided thatat least one of R₁ and R₂ is hydrogen;

wherein R₁ and R₂ defined above can be unsubstituted or substituted;

wherein R₃ is independently selected from the group consisting ofhydrogen, alkenyl, alkynyl cycloalkyl, aryl, alkylaryl, heteroaryl,alkylheteroaryl and heterocyclyl, any of which can be substituted orunsubstituted;

wherein R₄ is independently selected from the group consisting ofhydrogen, alkyl, alkenyl, alkynyl, cycloalkyl, aryl, alkylaryl,heteroaryl, and heterocyclyl, any of which can be substituted orunsubstituted;

wherein R₅ is selected from the group consisting of CCl₃, CF₃ and COOH;and

wherein x is 0-16, n is 0-10 and m is 2-1.0;

or a salt thereof.

Particularly preferred lipoic acid derivatives of the third embodimentinclude:

In a fourth embodiment, the present invention is directed to a lipoicacid derivative having formula (I):

wherein R₁ and R₂ are independently selected from the group consistingof alkyl sulfide defined as CH₃(CH₂)_(n)—S— and hemiacetal defined asR₅CH(OH)—S—;

wherein R₁ and R₂ as defined above can be unsubstituted or substitutedand wherein at least one of R₁ and R₂ is substituted;

wherein R₅ is selected from the group consisting of CCl₃, CF₃ and COOH;and

wherein x is 0-16, n is 0-10 and m is 2-10;

or a salt, thereof.

In a fifth embodiment, the present invention is directed to a lipoicacid derivative having formula (I):

wherein R₁ and R₂ are independently selected from the group consistingof acyl defined as R₃C(O), alkyl defined as C_(n)H_(2n+1), alkenyldefined as C_(m)H_(2m−1), alkynyl defined as C_(m)H_(2m−1), aryl,heteroaryl, alkyl sulfide defined as CH₃(CH₂)_(n)—S—, imidoyl defined asR₄C(═NH)—, and hemiacetal defined as R₅CH(OH)—S—;

wherein R₁ and R₂ as defined above can be unsubstituted or substituted;

wherein R₃ and R₄ are independently selected from the group consistingof hydrogen, alkyl alkenyl, alkynyl, cycloalkyl, aryl, alkylaryl,heteroaryl and heterocyclyl, any of which can be substituted orunsubstituted;

wherein R₅ is selected from the group consisting of CCl₃, CF₃ and COOH;and

wherein x is 0-16, n is 0-10 and m is 2-10;

provided that at least one of R₁ and R₂ is independently selected fromthe group consisting of an alkyl sulfide defined as CH₃(CH₂)_(n)—S— andhemiacetal defined as R₅CH(OH)—S—, said at least one of R₁ and R₂ beingsubstituted; at a salt thereof.

Particularly preferred lipoic acid derivatives of the fourth and fifthembodiments, include:

In a sixth embodiment of this invention, the lipoic acid derivative hasthe formula (II):

M is —[C(R₁)(R₂)]_(z)—, where R₁ and R₂ are independently selected fromthe group consisting of acyl defined as R₃C(O)—, alkyl defined asC_(n)H_(2n+1), alkenyl defined as C_(m)H_(2m−1), alkynyl defined asC_(m)H_(2m−3), aryl, heteroaryl, alkyl sulfide defined asCH₂(CH₂)_(n)—S—, imidoyl defined as R₃C(═NH)—, hemiacetal defined asR₄CH(OH)—S— and hydrogen, wherein R₁ and R₂ as defined above can beunsubstituted or substituted. R₃ and R₄ are independently selected fromthe group consisting of hydrogen, alkyl, alkenyl, alkynyl, cycloalkyl,aryl, alkylaryl, heteroaryl, and heterocyclyl, any of which can besubstituted or unsubstituted; R₅ is selected from the group consistingof CCl₃, CF₃ or COOH. In addition, x is 0-16, z is preferably 0-5, morepreferably 0-3, n is 0-10 and m is 2-10. Suitable —C(R₁)(R₂)_(z)— groupsinclude, without limitation, —CH₂, —CH(CH₃), —C(CH₃)₂, —CH(C₆H₅) and—CH(pyridine).

Particularly preferred lipoic acid derivatives of the sixth embodimentinclude:

As used herein, acyl refers to an R₃C(O)— group, where R₃ can be,without limitation, hydrogen, alkyl, alkenyl alkynyl, cycloalkyl, aryl,alkylaryl, heteroaryl, or heterocyclyl, any of which can be substitutedor unsubstituted. In certain embodiments of the invention, R₃ ishydrogen, alkenyl, alkynyl, alkylaryl heteroaryl, alkylheteroaryl ororganometallic aryl, any of which can be substituted or unsubstituted;in other embodiments, R₃ is hydrogen, alkenyl, alkynyl, cycloalkyl,aryl, alkylaryl, heteroaryl, alkylheteroaryl, or heterocyclyl, any ofwhich can be substituted or unsubstituted. In other words, one of thelisted R₃ groups is linked to the carbon backbone of formula (I) througha thio-ester linkage. Examples of acyl groups include, withoutlimitation, acetyl, benzoyl and benzoyl derivatives, 4-fluorobenzoyl and1-methylpyrrole-2-carboxyl.

As used herein, alkyl refers to a C_(n)H_(2n+1) group, wherein n is1-10, more preferably 1-6 and most preferably 1-4, i.e., an alkyl grouplinked to the carbon, backbone of formula (I) through a thio-etherlinkage. Alkyl groups can be either aliphatic (straight, or branchedchain) or alicyclic; alicyclic groups may have additions orsubstitutions on any of the carbons to form heterocyclics. At least oneheteroatom such as N, O or S may be present in a given alkyl group,i.e., in the carbon chain. Alkyl groups may be substituted orunsubstituted on any of their carbons. A preferred alkyl group is analkyl group substituted with an aryl or heteroaryl group, i.e., whereinR₁ or R₂ is an alkylaryl or alkylheteroaryl group; the aryl orheteroaryl group may be substituted or unsubstituted. Examples of alkylgroups include, without limitation, methyl, ethyl, butyl, decanyl,cyclopropyl, 4-pyridine methyl, 2-anthraquinone methyl,N-phenylacetamide, phenylethyl, 2-ethanoic acid, 2-acetamide,4-(2-acetamido-pyridinyl)methyl, N-[(2-fluorophenyl)methyl]acetamide,N-[(6-methoxy-3-pyridyl)methyl]acetamide,5-(acetylamino)pyridine-2-carboxamide,5-(6,8-diaza-7-oxo-3-thiabicyclo[3.3.0]oct-2-yl)-N-(2-carbonylaminoethyl)pentanamideand 5-(6,8-diaza-7-oxo-3-thiabicyclo[3.3.0]oct-2-yl)pentacarboxyl.

As used herein, alkenyl refers to a C_(m)H_(2m−1) group, wherein m is2-10, i.e., an alkenyl group linked to the carbon backbone of formula(I) through a thio-ether linkage. Alkenyl groups can be either aliphatic(straight or branched chain) or alicyclic; alicyclic groups may haveadditions or substitutions on any of the carbons to form heterocyclics.At least one heteroatom such as N, O or S may be present in a givenalkenyl group, i.e., in the carbon chain. Alkenyl groups may besubstituted or unsubstituted on any of their carbons. Examples ofalkenyl groups include, without limitation, propenyl, 2,3dimethyl-2-butenyl, heptenyl and cyclopentenyl.

As used herein, alkynyl refers to a C_(m)H_(2m−3) where m is 2-10, i.e.,an alkynyl group linked to the carbon backbone of formula (I) through athio-ether linkage. Alkynyl groups can be either aliphatic (straight orbranched chain) or alicyclic; alicyclic groups may have additions orsubstitutions on any of the carbons to form heterocyclics. At least oneheteroatom such as N, O or S may be present in a given alkynyl group,i.e., in the carbon chain. Alkynyl groups may be substituted orunsubstituted on any of their carbons. Examples of alkynyl groupsinclude, without limitation, acetylenyl, propynyl and octynyl.

As used herein, aryl refers to an aromatic or aryl group linked to thecarbon backbone of formula (I) through a thio-ether linkage. Aryl ispreferably an unsaturated ring system having 6-10 carbon atoms. Arylalso includes organometallic aryl groups such as ferrocene. Aryl groupsmay be substituted or unsubstituted on any of their carbons. Examples ofaryl groups include, without limitation, benzyl (—CH₂C₆H₅), benzylderivatives such as methylbenzyl and aminobenzyl,(1,2,3,4,5-pentafluorophenyl)methyl, triphenylmethyl, 4-methyl benzoicacid, ferrocene methyl, 2-naphthylmethyl, 4,4-biphenylmethyl, andstilbene (or 1-((1E)-2-phenylvinyl)-4-methyl benzene).

As used herein, heteroaryl refers to an aromatic heterocyclic ringsystem (monocyclic or bicyclic) where the heteroaryl moieties are five-or six-membered rings containing 1 to 4 heteroatoms selected from thegroup consisting of S, N, and O; the heteroaryl group is linked to thecarbon backbone of formula (I) through a thio-ether linkage. Heteroarylgroups may be substituted or unsubstituted on any of their atomsespecially on the carbon atoms. Examples of heteroaryl groups include,without limitation, benzothiatazole, quinoline, 7-chloroquinoline,furan, thiophene, indole, azaindole, oxazole, thiazole, isoxazole,isothiazole, imidazole, N-methylimidazole, pyridine, pyrimidine,pyrazine, pyrrole, N-methylpyrrole, pyrazole, N-methylpyrazole,1,3,4-oxadiaisple, 1,2,4-triazole, 1-methyl-1,2,4-triazole,1H-tetrazole, 1-methyltetrazole, benzoxazole, benzofuran, benzisoxazole,benzimidazole, N-methylbenzimidazole, azabenzimidazole, indazole,quinazoline and pyrrolidinyl.

As used herein, alkyl sulfide refers to a CH₃(CH₂)_(n)—S— group, where nis 0-9. In other words, an alkyl group is linked to the carbon backboneof formula (I) through a disulfide linkage. The alkyl group (i.e.CH₃(CH₂)_(n)) can be substituted or unsubstituted on any of its carbonsand shares the same features as set forth above with regard to theC_(n)H_(2n+1) alkyl group.

As used herein, imidoyl refers to a R₄C(═NH)— group, where R₄ can be,without limitation, hydrogen, alkyl, alkenyl, alkynyl, cycloalkyl, aryl,alkylaryl heteroaryl, or heterocyclyl, any of which can be substitutedor unsubstituted. In certain embodiments of the invention, R₄ ishydrogen, alkenyl, alkynyl, aryl, alkylaryl, heteroaryl andalkylheteroaryl, any of which can be substituted or unsubstituted. Inother words, one of the listed R₄ groups is linked to the carbonbackbone of formula (I) through a thio-imide linkage.

As used herein, hemiacetal refers to an R₅CH(OH)—S— group, where R₅ is acompound with a strongly electron withdrawing substituent such as,without limitation, CF₃, CCl₃ or COOH.

Any of the above-described groups can be unsubstituted or substituted.Exemplary substituents include, without limitation, alkyl, alkenykalkynyl, aryl, heteroaryl, acyl, alkoxycarbonyl, alkoxy, alkoxyalkyl,alkoxyalkoxy, cyano, halogen, hydroxy, nitre, oxo, trifluoramethyl,trifluoromethoxy, trifluoropropyl, amino, amido, alkylamino,dialkylamino, dialkylaminoalkyl, hydroxyalkyl, alkoxyalkyl, alkythio,—SO₃H, —SO₂NH₂, —SO₂NHalkyl, —SO₂N(alkyl)₂, —CO₂H, CO₂NH₂, CO₂NHalkyl,and —CO₂N(alkyl)₂. In addition, any number of substitutions may be madeon any of the above-described groups; in other words, it is possible tohave a mono-, di-, tri-, etc. substituted R₁ or R₂ group, and thesubstituents themselves may also be substituted. Further, any Of the R₁or R₂ groups may be appropriately generally substituted with any of acarbohydrate, a lipid, a nucleic acid, an amino acid or a polymer of anyof those, or a single or branched chain synthetic polymer (having amolecular weight ranging from about 350 to about 40,000).

For any definition of R₁ and R₂ noted above, the thio-ester ,orthio-ether linkage, by which the R₁ and R₂ are linked to the backbonecan be oxidized to produce sulfoxides or sulfones; in other words,: the—S— in the linkage, could be —S(O)— or —S(O)₂. In addition, for anydefinition of R₁ and R₂ noted above, the thio-ester or thio-etherlinkage by which the R₁ and R₂ are linked to the backbone may furthercomprise disulfides that can be oxidized to thiosulfinic or thiosulfonicacids; in other words, instead of —S— in a linkage, the linkage could be—S(O)—S— or —S(O)₂—S—.

Regardless of whether the lipoic acid derivative is of formula (I) orformula (II), lipoic acid, derivatives of the present invention mayinclude those in which one or both of the thiols have been replaced witha selenium molecule, a sulfur analog, or in which one or both of thethiols have been oxidized to sulfate or related groups.

Additional preferred lipoic acid derivatives of the present inventioninclude certain, compounds of formula (I) in which an alkylarylsubstituent for one or both of R₁ and R₂ is present. Such lipoic acidderivatives include:

Still other preferred embodiments of the present invention, include thefollowing lipoic acid derivatives in which an alkyl group with aheteroatom substitution is present for one or both of R₁ and R₂:

Another preferred embodiment, of the present invention is directed tothe following lipoic acid derivative which includes a substituted acylgroup:

Still additional preferred embodiments of the present invention includethe following asymmetrically substituted lipoic acid derivatives:

A further embodiment of the present invention is directed to apharmaceutical formulation comprising (a) a therapeutically effectiveamount of at least one lipoic acid derivative of any one of thepreviously set forth (above) embodiments and (b) at least onepharmaceutically acceptable additive.

Typically the at least one lipoic acid derivative is present in apharmaceutical formulation of the present invention in a therapeuticallyeffective amount. The pharmaceutical formulation of the presentinvention, may contain a unit dose or multiple doses of the lipoic acidderivative. A “therapeutically effective amount” is intended to mean theamount of a lipoic acid derivative that, when administered to a subjectin need thereof, is sufficient to effect treatment for (or prevent)disease conditions characterized by disease cells that are sensitive tolipoic acid derivatives. The amount of a given lipoic acid derivativethat will be therapeutically effective will vary depending Upon factorssuch as the disease condition and the severity thereof, the identity ofthe subject in need thereof, etc., which amount may be routinelydetermined by artisans of ordinary skill in the art. Importantly, thequantity of lipoic acid derivative in a unit dose should be sufficientto inhibit or kill tumor cells while leaving normal cells substantiallyunharmed. The at least one lipoic acid derivative is preferably presentin a pharmaceutical formulation of the present invention in an amount toprovide from about 0.001 mg/m² to about 10 g/m², more preferably about0.01 mg/m² to about 5 g/m², still more preferably from about 0.25 mg/m²to about 3 g/m², and most preferably from about 20 mg/m ² to about 500mg/m² of the at least one lipoic acid derivative per dose.

Pharmaceutically acceptable additives suitable for use in the presentinvention include, without limitation, solvents, diluents, surfactants,solubilizers, preservatives, buffers, and combinations thereof, as wellas any other additives particularly suited for use in parenteraladministration forms. It is well within the skill of one of ordinaryskill in the art to determine suitable amounts of these pharmaceuticallyacceptable additives. Solvents particularly suitable for use hereininclude benzyl alcohol dimethylamine, isopropyl alcohol and combinationsthereof; one of ordinary skill in the art would readily recognize thatit may be desirable to first dissolve the at least one lipoic acid,derivative in a suitable solvent and then to dilute the solution with adiluent.

When a pharmaceutical formulation suitable for, e.g., intravenousadministration is desired, a suitable diluent would be employed. Anyconventional aqueous or polar aprotic solvent is suitable for use in thepresent invention. Suitable pharmaceutically acceptable diluentsinclude, without limitation, saline, a sugar solution, alcohols such asethyl alcohol, methanol and isopropyl alcohol, polar aprotic solventssuch as dimethylformamide (DMF), dimethylsulfoxide (DMSO) anddimethylacetamide (DMA), and combinations thereof. A preferredpharmaceutically acceptable diluent is a dextrose solution, morepreferably a dextrose solution containing from about 2.5% to about 10%,more preferably about 5%, dextrose by weight. The pharmaceuticallyacceptable diluent is typically employed in a non-homolysis generatingamount; one of ordinary skill in the art can readily determine an amountof diluent suitable for use in a pharmaceutical formulation according tothe present invention.

The pharmaceutical formulations of the present invention can be preparedaccording to conventional formulation techniques. For example, a stocksolution of the at least one lipoic acid derivative can be preparedaccording to conventional techniques and then diluted as desired by apharmaceutically acceptable diluent. Pharmaceutical formulations of thelipoic acid derivatives of the present invention may also be prepared inaccordance with the details set forth in co-pending U.S. ProvisionalApplication No. 60/912,605, filed Apr. 18, 2007 [Attorney Docket. No.03459.000100.PV] and corresponding co-pending U.S. patent applicationSer. No. xx/xxx,xxx, filed Apr. xx, 2008, the entire disclosure of whichis incorporated by reference herein.

The pharmaceutical formulations of the present invention are liquidpreparations such as sterile parenteral solutions. The pharmaceuticalformulations of the present invention may be contained in any suitablevessel such as a vial or ampoule and ate suitable for administration viaone of several routes including, without limitation, intravenous,intramuscular, subcutaneous, intradermally, intraperitoneal,intrathoracic, intrapleural, intrauterine or intratumor.

Further embodiments of the invention are directed to pharmaceuticalformulations which are suitable for types of administration other thanthose listed above, for example and without limitation, oral, nasal,topical, transdermal, and rectal. The pharmaceutical formulations ofthis invention may take any pharmaceutical form recognizable to theskilled artisan as being suitable. Suitable pharmaceutical forms includesolid, semisolid, liquid, or lyophilized formulations, such as tablets,powders, capsules, suppositories, suspensions, liposomes, and aerosols.

A further embodiment of the invention is directed to a method oftreating a disease characterized by disease cells that are sensitive tolipoic acid derivatives comprising administering to a patient in needthereof a therapeutically effective amount of at least one lipoic acidderivative according to the present invention. Preferably, the at leastone lipoic acid derivative is incorporated into a pharmaceuticalformulation according to the present invention. A still furtherembodiment of the invention is directed to a method of preventing adisease characterized by disease cells that are sensitive to lipoic acidderivatives comprising administering to a patient in need thereof atherapeutically effective amount of at least one lipoic acid derivativeaccording to the present invention. Preferably, the at least one lipoicacid derivative is incorporated into a pharmaceutical formulationaccording to the present invention.

According to the methods of treatment and prevention, lipoic acidderivatives and pharmaceutical formulations of lipoic acid derivativesof the present invention may be used to prevent or inhibit diseasesinvolving altered or distinct cellular PDC activity, i.e., diseasescharacterized by disease cells that are sensitive to lipoic acidderivatives. Cells with appropriately altered or deranged energymetabolism, i.e., altered PDC activity, are particularly targeted andkilled, while surrounding healthy tissues remain unharmed by the lipoicacid derivative. The skilled artisan can readily identify diseaseshaving altered PDC activity: Alternatively, the skilled artisan canreadily screen the disease of interest for sensitivity to lipoic acidderivatives.

In preferred embodiments of the methods of the present invention, thedisease treated or prevented includes cancer, such as carcinoma,sarcoma, myeloma, lymphoma, leukemia and mixed types thereof. Thepharmaceutical formulations of the present invention are effectiveagainst both primary and metastatic cancers and effective againstcancers of the, without limitation, lung, liver, uterus, cervix,bladder, kidney, colon, breast prostate, ovary, and pancreas. In otherembodiments, the pharmaceutical formulations of the present inventioncan be used in the treatment of diseases associated with altered energymetabolism such as Alzheimer's disease, hyperproliferative diseases suchas psoriasis and other diseases such as diabetic neuropathy.

For therapeutic applications, a lipoic acid derivative or apharmaceutical formulation according to the invention is administereddirectly to a patient, typically in a unit dose form. In the methods ofthis invention, the lipoic acid derivative or pharmaceutical formulationcomprising the lipoic acid derivative may be administered via one ofseveral routes including, without limitation, intravenous,intramuscular, subcutaneous, intradermally, intraperitoneal,intrathoracic, intrapleural, intrauterine or intratumor. Those skilledin the art will recognize that the mode of administering the lipoic acidderivative depends on the type of cancer or symptom to be treated. Forexample, a preferred mode of administering the lipoic acid for treatmentof leukemia would involve intravenous administration. Likewise, thoseskilled in the art will also recognize that particular pharmaceuticallyacceptable additives will vary from pharmaceutical formulations suitablefor one administration mode to pharmaceutical formulations suitable foranother administration mode.

By adapting the treatments described herein, the lipoic acid derivativesor the pharmaceutical formulations of the present invention may also beused in methods for treating diseases other than cancer, where thedisease-causing cells exhibit altered metabolic patterns. For example,eukaryotic pathogens of humans and other animals are generally much moredifficult to treat than bacterial pathogens because eukaryotic cells areso much more similar to animal cells than are bacterial cells. Sucheukaryotic pathogens include protozoans such as those causing malaria aswell as fungal and algal pathogens. Because of the remarkable lack oftoxicity of the lipoic acid derivatives of the invention to normal humanand animal cells and became many eukaryotic pathogens are likely to passthrough life cycle stages in which their PDCs become sensitive to lipoicacid derivatives, the lipoic acid derivatives and pharmaceuticalformulations of the present invention can be used to kill bacterialPDCs.

Specific embodiments of the invention will now be demonstrated byreference to the following examples. It should be understood that theseexamples are disclosed solely by way of illustrating the invention andshould not be taken in any way to limit the scope of the presentinvention.

Synthesis of 6,8-Bismercaptooctanoic Acid (Intermediate)

α-Lipoic acid (5.15 g, 25.0 mmol) was suspended in water (125 mL), andsodium bicarbonate (2.1 g, 25.0 mmol) was added. The mixture was stirredto produce a clear solution. The resulting pale yellow solution wascooled in an ice bath, and solid sodium borohydride (1.90 g, 50.0 mmol)was added, with stirring. in small portions over 20 min. The solutionwas stirred in an ice bath for another 30 min and then at roomtemperature for 30 min. The cloudy solution was copied in an ice bath,and the pH was adjusted to 1 by stow addition of 2M hydrochloric acid. Avigorous evolution of hydrogen occurred as the excess sodium borohydridedecomposed, and an oily liquid was seen to separate. The mixture wasextracted with chloroform (3×50 mL). The combined chloroform extractswere dried ever magnesium sulfate, filtered and the solvent evaporatedunder reduced pressure at room temperature. The remaining oil wasfurther dried under vacuum to remove traces of solvent.6,8-Bismercaptooctanoic acid was isolated as a colorless oil; 5.2 g(100%). The product was stored at −20° C. under nitrogen. ¹H-NMR(CDCl₃); δ2.89 (m, 1 H, S—C—H), 2.67 (m, 2H, S—CH₂), 2.34 (t, J=7.1 Hz,2H, CH₂C(O)), 1.4-1.92 (m, 8H, (CH₂)₂), 1.33 (t, J=8.0 Hz, 1 H, S—H),1.30 (t, J=7.6 Hz, 1 H, S—H).

Example 1 General Procedure for Compounds (A), (E) and (F)

6,8-Bismercaptooctanoic acid (1 eq.), obtained as described above, wasdissolved in absolute ethanol. To this: solution, the appropriate arylchloride (2.2 eq.) was added. The resulting solution was treated with afreshly prepared sodium ethoxide solution (sodium (4.4 eq.) was added insmall portions, under nitrogen, to absolute ethanol to form freshlyprepared sodium ethoxide). The reaction mixture was refluxed undernitrogen for 4-6 h. The reaction mixture was then cooled in an ice bathand acidified carefully with 2N HCl, to a pH of 2-3. The acidic aqueousphase was extracted with chloroform (×3), and the combined chloroform,extracts were washed with water (×1), sat. aq. NaCl (×1), and dried(MgSO₄). Evaporation of the chloroform gave the crude product. Theproducts were purified by column chromatography on silica gel withchloroform:methanol (9:1) as the eluent.

For compounds obtained as sodium salts, the acidification step describedabove was omitted. The reaction mixture, upon evaporation of thesolvents, was dissolved in chloroform, and ether was added toprecipitate the sodium salt which was filtered and dried in vacuo.

Example 2 General Procedures for S-Acylated Compounds (C), (D) and (GG)

Procedure 1: 6,8-Bismercaptooctanoic acid was acylated with threeequivalents of the appropriate acyl chloride in the presence oftriethylamine to produce 6,8-bisacylmercaptooctanoic acylanhydride. Theanhydride was selectively hydrolyzed with dioxane/water to produce6,8-bis-acylmercaptooctanoic acid without any undesired hydrolysis ofthe benzoyithio ester groups. The product was purified by columnchromatography on silica gel.

General example of procedure 1—synthesis of6,8-bisbenzoylmercaptooctanoic acid: 6,8-Bismercaptooctanoic acid (2.03g, 10 mmol) was dissolved in dry methylene chloride (50 mL) undernitrogen, and triethylamine (3.24 g, 32 mmol) was added. Benzoylchloride (4.50 g, 32 mmol) in methylene chloride (20 mL) was addeddropwise, with stirring, over 20 min. The salt that was formed betweentriethylamine and HCl precipitated during this addition. The solutionitself remained colorless. Stirring was continued at room temperaturefor 9 h. The volume was increased to 100 mL with more methylene chloride(the entire solid dissolved), and the solution was transferred to aseparatory funnel. It was extracted with 10% citric acid (2×50 mL, thepH of the aqueous-phase was checked after the extraction to be sure itwas acidic), and then washed with saturated aq. NaCl (50 mL). Theorganic phase was dried over magnesium sulfate, filtered, and themethylene chloride evaporated. A colorless oil was obtained. The aboveoil (5.48 g) was dissolved in dioxane (20 mL), and water (20 mL) wasadded. This caused the material to form an oil. The mixture was stirredat 40-45° C. for 53 h. The solvent was evaporated under vacuum (2 mm) at30° C. The remaining oil was dissolved in chloroform (50 mL) andextracted with 5% aqueous citric acid (20 mL). The organic phase wasdried over magnesium sulfate, filtered, and the solvent evaporated. Afaint yellow oil was isolated (5.7 g). NMR spectra indicated that onlyabout one third of the anhydride had teen hydrolyzed. The crude materialwas re-dissolved in dioxane (20 mL) and wafer (10 mL), This mixture wasstirred at 45° C. for 32 h. The solvents were evaporated in vacuo. NMRindicated that the hydrolysis of the anhydride was complete. The productwas suspended in ethyl acetate (2 mL) and applied to a 25×4.5 cm columnof silica gel 60 (150 g) equilibrated with hexane—ethyl acetate—aceticacid (100:50:1, v/v). The column was then eluted with the same solventmixture. Fractions of 40 mL were collected at about 5 mL/min.Pure-product was collected in fractions 16-21: (1.95 g, colorless oil):1H-NMR (CDCl3); δ 8.0 (m, 4H, Aromatic H), 7.38-7.60 (m, 6H, AromaticH), 3.89 (m, 1H, CH—S), 3.0-3.3 (m, 2H, CH2S), 2.34 (t, J=7.1 Hz, 2H,CH2C(O)), 1.1-2.2 (m, 8H, CH2); 13C-NMR (CDCl3); δ 191.71, 191.46,179.72, 136.98, 136.92, 133.29, 128.51, 127.25, 127.14, 43.60, 34.98,34.59, 33.76, 26.43, 26.19, 24.29; TLC (hexane-ethyl acetate—aceticacid, 100:50:1, v/v), Rf=0.30; IR (neat): 2937, 1710, 1704, 1662, 1667,1655, 1448, 1207, 1175, 911, 773, 757, 733, 648, 688 cm⁻¹.

Procedure 2: 6,8-Bismercaptooctanoic acid was acylated with 1.2 eq. ofthe appropriate carboxylic acid which had been pre-activated with CDI(1.2 eq.) in DCM in the presence of triethylamine (1.2 eq.). Theproducts were purified by column chromatography on silica gel asdescribed above.

Compound (K) was isolated during chromatography, as a side-productduring the synthesis of compound (D).

Example 3 General Procedure for Thioacetal Compounds (M), (N), (O), (P)and (Q)

The thioacetal compounds (M)-(Q) were synthesized by adapting thegeneral procedures described in J. Am. Chem. Soc. 1993, 115, 3458 and J.Org. Chem. 1975, 40,231:

To 6,8-bismercaptooctanoic acid (1 eq.) in DCM under a nitrogenatmosphere, was added the appropriate aldehyde or ketone (1 eq.). Themixture was stirred at room temperature for 1 h and cooled to −25° C.BF3 etherate (1 eq.) was added, and the reaction was allowed to warm toroom temperature. After evaporation of the solvent, the products werepurified either by crystallization or by chromatography on silica gelwith ethyl acetate:hexane (1:2) as the eluent.

Example 4 General Procedure for Bis-Alkylated Compounds (S), (T), (U),(V), (W), (X), (BB) and (II)

To 6,8-Bismercaptooctanoic acid (1 eq.) in THF under a nitrogenatmosphere, the appropriate benzyl bromide, the phenethyl bromide or thealkyl bromide (2 eq.) was added. Freshly prepared sodium ethoxide (3eq.) in absolute ethanol was added dropwise, with stirring over 10 min.The reaction mixture was then refluxed for 5.5 h and cooled to roomtemperature. After dilation with water, the solution was cooled in iceand acidified with 2N HCl to pH=2. The product was extracted withchloroform (×3), and the combined organic extracts were washed withwater (×1), saturated aq. NaCl (×1), and dried (MgSO4). Evaporation ofthe solvent gave the crude product which was crystallized from benzeneand hexane or purified by column chromatography on silica gel with 1-3%methanol in DCM.

Example 5 Synthesis of Compound (B)

Compound (B) was synthesized using a method adapted from Org. Lett.2007, 6, 3687; 6, 8-Bismercaptooctanoic acid (1 eq.) andferrocenemethanol (2.1 eq.) in DCM were treated with trifluoroaceticacid (6.5 eq.) at room temperature for 1 h. The solvent was removed, andthe crude product was purified by using column chromatography on silicagel (hexane:ethyl acetate 2:1).

Example 6 Synthesis of (Intermediate) Compound (1)

6,8-Bismercaptooctanoic acid (1.04 g, 5.0 mmol) was dissolved intrifluoroacetic acid (10 mL), under nitrogen. To this stirred solution,triphenylmethanol (1.30 g, 5.0 mmol) was added in small portions. Thesolution was stirred for 15 min and evaporated by using vacuum (2 mm at10° C.). The resulting residue was dissolved in fresh trifluoroaceticacid (7 mL) and was stirred for 10 min. The solvent was removed undervacuum, and any remaining trifluoroacetic acid was removed byazeotroping with dry benzene (3×2 mL). TLC analysis of the residualviscous syrup (CHCl₃:CH₃OH:CH₃COOH. 100:10:1) revealed three spots withRf values of 0.42, 0.47 and 0.54. The major spot had a Rf value of 0.47.The crude material was dissolved in chloroform (1 mL) and applied to acolumn (36×3.2 cm) which had been pressure-packed with silica gel (14%),in CHCl₃:CH₃OH:CH₃COOH, 100:5:1. It is important that the column bepacked very well and at least 100 g of silica be used for every gram ofthe reduced lipoic acid starting material. The column was initiallyeluted with the initial solvent mixture (100 mL). The column was theneluted with CHCl₃:CH₃OH:CH₃COOH (100:7:1). Fractions of 20 mL werecollected at 2 mL/min. Reasonably pure product was collected infractions 10-16 to yield 1.44 g. This6-mercapto-8-tritylmercaptooctanoic acid was used to synthesizecompounds (Y), (Z) and (AA).

Example 7 General Procedure for Compounds (Y) and (Z)

Syntheses of compounds (Y) and (Z) can be exemplified by the followinggeneral procedure for the synthesis of6-ethylmercapto-8-tritylmercaptooctanoic acid, compound (Z): Compound(J) (1.09 g, 2.4 mmol) was dissolved in absolute ethanol (40 mL), andethyl bromide (0.38 g, 3.0 mmol) was added. The stirred solution wasplaced under an atmosphere of nitrogen, and a solution of sodiumethoxide (10 mmol) in absolute ethanol (10 mL) was added over 5 min(this solution was freshly prepared by reacting sodium metal (0.23 g)with the ethanol). The solution was stirred at room temperature for 20min. It was then heated under gentle reflux for 6 h (bath temp 95° C.).A white solid was seen precipitating during this time. The mixture wascooled to room temperature, and the ethanol was evaporated in vacuo (1mm at 10° C.). The residue was suspended in water (40 mL). The pH wasadjusted to about 2 (pH paper) with 2M hydrochloric acid. The mixturewas extracted with ethyl acetate (3×25 mL). The combined extracts werewashed with saturated aq. NaCl (20 mL) and dried over magnesium sulfate.The solvent was evaporated to yield a yellow viscous oil weighing 1.14g. The crude material in chloroform (2 mL) was applied to a column(25×3.2 cm) packed with silica gel of (90 g) in CHCl₃—CH₃OH—CH₃COOH,250:10:1. Elation with this solvent yielded 0.85 g (74.5%) of a yellowsyrup.

Example 8 Synthesis of Compound (AA)

Compound (J) (6-Mercapto-8-trityl-bismercaptooctanoic acid) (1.36 g, 3.0mmol) was dissolved in absolute ethanol (50 mL), and bromoacetic acid(0.63 g: 4.5 mmol) was added. The colorless solution was treated with asolution of sodium ethoxide (12 mmol) in absolute ethanol (10 mL) (thissolution was freshly prepared by reacting sodium metal (0.28 g) withethanol). A white solid formed upon addition. The mixture was stirred atroom temperature for 30 min and then under gentle reflux for 7 hr (bathtemperature 95° C.). The mixture was cooled to room temperature, and thesolvent was evaporated under vacuum at room temperature to yield a paleyellow solid. The solid, was dissolved in water (50 mL). The pH wasadjusted to about 2 with 2M hydrochloric acid. A slightly yellowprecipitate formed. The mixture was extracted with ethyl acetate (4×25mL). The combined extracts were washed with saturated brine (20 mL). Thesolution was dried over magnesium sulfate, filtered and the solventevaporated to yield a pale yellow viscous oil (1.59 g). TLC (Silica gel,100:10:1 CHCl₃—CH₃OH—CH₃COOH) showed a major spot with Rf=0.42. Thecrude material was dissolved in chloroform (2 mL) and applied to acolumn (24×3.2 cm) that had been pressure-packed with silica gel (90 g)in CHCl₃—CH₃OH—CH₃COOH (100:5:1). The column was then eluted withCHCl₃:CH₃OH:CH₃COOH (100:10:1). Fractions (20 mL) were collected at 2mL/min. The product was collected in fractions 14-20 to yield acolorless oil, 1.32 g (75% after correcting for residual acetic acid).

Example 9 General Procedure for Compounds (G), (H) and (L)

The synthesis of compounds (G) and (H) can be exemplified by thefollowing general procedure for 6-ethylmercapto-8-mercaptooctanoic acid(compound (H)): 6-Ethylmercapto-8-trityl-bismercaptooctanoic acid (0.85g, 1.78 mmol) was dissolved in trifluoroacetic acid (10 mL). A deepyellow solution resulted. Triethylsilane (0.42 g, 0.58 mL, 3.6 mmol,)was added in one portion. A white solid was seen precipitating. Themixture was left at room temperature with occasional swirling for 10min. The solid was removed by filtration and washed with trifluoraceticacid (2×2 mL). The combined filtrates were evaporated to dryness invacuo at room temperature and then azeotroped with benzene (2 mL) toyield an oil (0.49 g). TLC (silica gel, CHCl₃—CH₃OH-CH₃COOH (100:5:1))showed two spots with Rf=0.82 (triphenylmethane) and 0.35 (product). Thecrude material was added onto a column (22×2.3 cm) packed with silicagel (40 g) in CHCl₃—CH₃OH—CH₃COOH (100:5:1). The column was eluted withthis solvent to yield the product as a faint tan syrup: 0.33 g (78%).The product was stored in the dark, under nitrogen or argon, at −20° C.

Similarly, compound (G) was synthesized from compound (Y). Compound (L)was synthesized by a similar three-step procedure as used for compounds(H) and (G).

Example 10 Synthesis of Compound (I)

Compound (AA), (6-Carboxymethylenemercapto-8-trityl-bismercaptooctanoicacid), was dissolved in trifluoroacetic acid. (12 mL). Triethylsilane(0.53 g, 0.73 mL, 4.6 mmol) was added in one portion. The bright yellowsolution became colorless, and a white solid precipitated. The mixturewas left at room temperature with occasional swirling for 10 min and wasfiltered. The solid was washed with trifluoroacetic acid (2×3 mL). Thecombined filtrates were evaporated to dryness under vacuum at roomtemperature and azeotroped with benzene (2 mL) to give a faint brown oil(0.74 g). The crude material was dissolved in chloroform (1 mL) andadded to a column (28×2.3 cm) packed with silica gel (40 g) inCHCl₃—CH₃OH—CH₃COOH (100:5:1). The column was eluted withCHCl₃—CH₃OH—CH₃COOH (100:7:1) to yield a viscous colorless syrup: 0.54 g(82%). The product should be stored in the dark, preferably undernitrogen, at −20° C. TLC: Rf=0.35 (100:7:1 CHCl₃—CH₃OH—CH₃COOH).

Example 11 General Procedure for Compounds (CC), (DD), (EE), (FF) and(HH)

Compounds (CC), (DD), (EE), (FF) and (HH) were synthesized by using theabove described procedures. Compound (J) was alkylated withbromoacetamide. The trityl protecting group was removed as describedabove to yield 6-acetamido-8-mercapto-6,8-bismercaptooctanoic acid. Thisintermediate was then alkylated With the appropriate alkyl bromides orbenzyl bromide (for compound (HH)) in the presence of sodium ethoxide inrefluxing ethanol as described previously.

Example 12 Synthesis of Compound MM(6-ethyl-8-phenyl-6,8-bismercaptooctanoic acid)

Cuprous iodide (12 mg) and anhydrous potassium carbonate (0.33 g, 2.4mmol) were placed in a tube (15×2 cm) equipped with a magnetic stirringbar, and 6-ethylmercapto-8-mercapto octanoic acid (Compound (H)) (0.19g, 0.8 mmol) in 2-methyl-2-butanol (2 mL) was added. The tube was closedwith a septum cap and flushed with argon. Ethylene glycol (100 mg, 90μL, 0.8 mmol) was added via a syringe followed by iodobenzene (164 mg,90 μL, 0.8 mmol,). The tube was flushed again with argon, then sealedwith parafilm and stirred at 95° C. for 38 h. The mixture was cooled toroom temperature, and water (15 mL) was added. The pH of the suspensionwas adjusted to 2 with 2.0 M hydrochloric acid. The mixture wasextracted with chloroform (3×10 mL). The combined extracts were driedover magnesium sulfate and filtered, and the solvent was evaporated toyield a yellow oil weighing 0.25 g, TLC (CHCl₃—CH₃OH—HOAc 100:10:1) andshowing a major spot with Rf=0.45, a minor spot with Rf=0.39 and severalminor spots. The erode product in chloroform (0.5 mL) was applied to acolumn (12×2.2 cm) with silica gel 60 (20 g) packed in CHCl₃—CH₃OH—HOAc(100:5:1). The column was eluted with CHCl₃—CH₃OH—HOAc (100:10:1).Fractions of 4-5 ml, were collected at a flow rate of 0.5 mL/min. Theproduct was collected in fractions 7-10; colorless oil weighing 140 mg.TLC Rf=0.45 (silica gel: CHCl₃—CH₃OH—HOAc, 100:10:1); ¹H-NMR (CDCl₃): δ7.1-7.4 (m, 5H), 3.08 (td, 2H), 2.6-2.8 (m, 1H), 2.48 (q, 2H), 2.35 (t,2H), 1.3-1.9 (m, 8H), 1.22 (t, 3H); MS (ESI (−)); 311 (M−1).

Example 13 Synthesis of Disulfide Compound (LL)

6,8-Bismercaptooctanoic acid (1.18 g, 5.67 mmol) in DCM (15 mL) andaldrithiol (5.0 g, 22.7 mmol, 4 eq.) were treated with a catalyticamount of glacial acetic acid (32.5 uL, 2.5 mol %). The reaction wasstirred at room temperature, under N₂, overnight. The solvent wasevaporated under reduced pressure, and the crude product was purified bycolumn chromatography on silica gel (80 g) with a solvent gradient ofhexane to 50% ethyl acetate in hexane. MS: 425 (M−1).

Example 14 Synthesis of Disulfide-Compound (JJ)

The bispyridyl-6,8-dithiooctanoic acid disulfide (1 eq.) obtained fromabove was dissolved in DCM, and benzyl mercaptan (2.5 eq.) was added.The reaction was initiated by adding a catalytic amount of acetic acid(2.5 mol %). After stirring overnight at room temperature, the solventwas evaporated, and the crude product was purified by columnchromatography on silica gel, with a solvent gradient of hexane to 50%ethyl acetate in hexane to elate the product. MS: 451 (M−1).

EXAMPLE 15

Synthesis of Compound (KK)

Aldrithiol (5.0 g, 22.6 mmol) in methanol (50 mL) was treated withacetic acid (33 uL, 0.565 mmol, cat.), and thiophenol (2.309 mL, 22.6mmol, 1 eq.) was added. The mixture was stirred at room temperature for24 h. The solvent was evaporated under reduced pressure, and the crudecompound was purified by column chromatography on silica gel (50 g),with hexane to 2% ethyl acetate in hexane as the eluent gradient:pale-yellow oil, 2.413 g (48.6%). This compound (500 mg, 2.279 mmol) wasreacted with Compound (L) (237.39 mg, 1.14 mmol, 1 eq.) in methanol (10mL), with acetic acid (3.5 uL, 0.057 mmol, cat.). The reaction wasstirred at room temperature for 24 h. The solvent was evaporated, andthe compound was purified by preparative thin-layer chromatography onsilica gel with 10% ethyl acetate in hexane as the developing solvent:pale yellow oil, 38 mg (9%), TLC (silica gel), Rf=0.18; MS (ESI (−)):423 (M−1).

EXAMPLE 16

Synthesis of Compound (R)

Compound (R) was synthesized using a combination of the monoS-alkylation procedure of Example 9 and the thioacetal formation, ofExample 3.

Testing

Three human tumor cells were used in this investigation, and they werehuman H460 NSCLC, human melanoma A2058 and human adenocarcinoma HT1080cell lines. Cells were originally obtained from American Type CellCulture (ATCC) and have been used for experiments at passages below 30.All tumor cells were maintained at 37° C. in a humidified 5% CO2atmosphere in T75 tissue culture flasks containing 25 mL of Roswell ParkMemorial Institute (RPMI) 1640, with 10% fetal bovine serum. (FBS) and 2mM L-glutamine. The tumor cells were split at a ratio of 1:10 every 4-5days by trypsinization and resuspended in fresh medium in a new flask.Cells were harvested for experiments at 70-90% confluency.

The culture media used for all cell lines in this study was Roswell ParkMemorial Institute (RPMI) 1640, with 10% fetal bovine serum (FBS), 2 mML-glutamine, 100 IU/mL penicillin and 100 μg/ml streptomycin. The testcompounds used were generally prepared at a concentration higher than 20mM and tested at 1 mM in cultured media for precipitation, 1 mM is thehighest tested concentration of the test compounds.

The anti-tumor activities of the test compounds were assessed byexposing the tumor cells to various concentrations of test compounds (orvehicle) or not treated with the test compounds or vehicle. Theconcentration ranges of the test compounds evaluated in this study were0-1 mM, The duration of treatment of the tumor cells was 48 hours.Subsequent to treatment with the test articles, the number of viabletumor cells was determined, and the concentrations of the test agentsthat induced 50% of cell growth inhibition (IC₅₀) were derived andcompared.

Cell Seeding for Experiments: To cells grown to 70-90% confluency,medium was removed and the cell monolayers were washed briefly by adding5 mL. of phosphate buffer saline. (PBS) followed by aspiration.Trypsin-ethylenediaminetetraacetic acid (EDTA) (4 mL) was added to each,flask, and the flask was placed in the tissue culture incubator for 5minutes. Serum-containing medium (10 mL) was added to halt the enzymaticreactions, and cells were disaggregated, by repeated resuspension withserological pipet. The cell-containing medium (20 μL) was added to 20 μLof 0.4% Trypan Blue solution, mixed, and 10 μL of this cell-containingmixture was placed in a chamber of a hemocytometer. The number of viablecells was determined by counting the number of viable cells (cells thatexcluded trypan blue) in the 4 corner squares of the hemocytometerchamber at 100× magnification. The volume of cells needed was determinedby the following formula:

${{{Volume}\mspace{14mu} {of}\mspace{14mu} {cells}\mspace{14mu} {needed}} = \frac{\# \mspace{14mu} {of}\mspace{14mu} {cells}\mspace{14mu} {wanted}\text{/}{mL}}{\# \mspace{14mu} {of}\mspace{14mu} {cells}\mspace{14mu} {counted}\text{/}{mL}}},$

where # of cells counted/mL=average # of cells on hemocytometer×2dilution factor×10⁴.

The number of cells targeted for the study was 4×10³ per well in 100 μLof medium. The actual number of cells were counted and seeded in thewells of a 96 well-plate. The cells were then incubated for 24 hrsbefore they were used for testing of anti-tumor activities of the testcompounds and vehicle. Cell monolayer was confluent or subconfluent forsome cell lines at the day of the experiment.

Treatment with Test Compounds and Vehicle: On the day of testing, 5 μLof a specific concentration of the test compounds (or vehicle) wereadded to the wells. After exposure to the test articles (or vehicle) for48 hours, the number of viable cells in the wells was determined (seenext section), and the percent of cells relative to no treatment wascalculated.

Determination of the Number of Viable Cells by the CellTiter Blue Assay:The number of viable cells was determined using the CellTiter Blue Assayin this study. Specifically, reagents were allowed to come to roomtemperature according to instructions from Protoega, Inc. (Madison,Wis.). CellTiter Blue reagent was added with the 12-channel Eppendorfpipettor, 20 μL per well. The cells were then incubated at 37° C. for1-4 hrs in cell culture incubator. Fluorescence intensity, which isproportional to the quantity of viable cells, was read at 530/590 nmusing FLUOstar optima fluorescence plate reader (BMG technologies,Germany).

Calculations of IC₅₀ Values: Data from fluorescence readings were copiedonto EXCEL spreadsheets, and cell growth relative to untreated cells wascalculated, using the following equation:

% #cells relative to untreated=(mean luminescence at N/mean fluorescenceuntreated)×100%

where N=concentration of the compound or vehicle.

The calculated values were imported into SigmaPlot, v9. A Four-ParameterLogistic Curve of the “mean relative cell growth as a function of theconcentrations of the test compounds” was generated. The IC₅₀ valueswere determined from the curves. The R-squared value provided anindication of the degree of fitness of data to the curve. The IC₅₀values for the tested compounds are set forth in Table 1 below.

TABLE 1 IC₅₀ A2058 IC₅₀ IC₅₀ (melanoma) H460 (NSCLC) HT1080 Compound(μM) (μM) (μM) A 183 ± 3  127 ± 11 80 ± 8  E 277 ± 9  234 ± 23 256 ± 19 F 51 ± 4   70 ± 13 68 ± 20 H 238 ± 2  282 ± 20 270 ± 4  Q 717 ± 11  nodata no data W 125 ± 3  167 ± 42 no data X 59 ± 4  64 ± 4 60 ± 18 JJ 206± 55  318 ± 20 133 ± 2  KK 483 ± 180 409 ± 69 212 ± 52  LL 745 ± 176 844 ± 176 737 ± 131 MM 346 ± 20  449 ± 1  421 ± 53 

While the invention has been described above with reference to specificembodiments thereof, it is apparent that many changes, modifications,and variations can be made without departing from the inventive conceptdisclosed herein. Accordingly, it is intended to embrace all suchchanges, modifications, and variations that fall within the spirit andbroad scope of the appended claims. All patent applications, patents,and other publications cited herein are incorporated by reference intheir entirety.

1. A lipoic acid derivative represented by the following formula:

wherein R₁ and R₂ are alkylaryl substituted by one or more halogen; x is0-16; or a salt thereof.
 2. The lipoic acid derivative of claim 1,wherein the lipoic acid derivative is

or a salt thereof.
 3. The lipoic acid derivative of claim 1, wherein thelipoic acid derivative is


4. A lipoic acid derivative, selected from, the group consisting of:

and a salt of either of the foregoing.
 5. The lipoic acid derivative ofclaim 4, wherein the lipoic acid derivative is

or a salt thereof.
 6. The lipoic acid derivative of claim 4, wherein thelipoic acid derivative is


7. A pharmaceutical formulation comprising a lipoic acid derivative ofclaim 1 and at least one pharmaceutically acceptable additive.
 8. Apharmaceutical formulation comprising a lipoic acid derivative of claim2 and at least one pharmaceutically acceptable additive.
 9. Apharmaceutical formulation comprising a lipoic acid derivative of claim3 and at least one pharmaceutically acceptable additive.
 10. Apharmaceutical formulation comprising a lipoic acid derivative of claim4 and at least one pharmaceutically acceptable additive.
 11. Apharmaceutical formulation comprising a lipoic acid derivative of claim5 and at least one pharmaceutically acceptable additive.
 12. Apharmaceutical formulation comprising a lipoic acid derivative of claim6 and at least one pharmaceutically acceptable additive.
 13. Thepharmaceutical formulation of claim 7, wherein the at least onepharmaceutically acceptable additive is selected from the groupconsisting of a solvent, diluent, surfactant, solubilizer, preservative,buffer, and combinations thereof.
 14. The pharmaceutical formulation ofclaim 8, wherein the at least one pharmaceutically acceptable additiveis selected from the group consisting of a solvent, diluent, surfactant,solubilizer, preservative, buffer, and combinations thereof.
 15. Amethod for treating a disease involving altered or distinct cellularpyruvate dehydrogenase complex (PDC) activity, comprising administeringto a patient in need thereof a therapeutically effective amount of acompound of claim 1 to treat said disease.
 16. The method of claim 15,wherein the disease is a cancer of the liver, uterus, cervix, bladder,kidney, colon, breast, prostate, ovary, or pancreas.
 17. A method fortreating a disease involving altered or distinct cellular pyruvatedehydrogenase complex (PDC) activity, comprising administering to apatient in need thereof a therapeutically effective amount of a compoundof claim 2 to treat said disease.
 18. The method of claim 17, whereinthe disease is a cancer of the liver, uterus, cervix, bladder, kidney,colon, breast, prostate, ovary, or pancreas.
 19. A method for treating adisease involving altered or distinct cellular pyruvate dehydrogenasecomplex (PDC) activity, comprising administering to a patient in needthereof a therapeutically effective amount of a compound of claim 4 totreat said disease.
 20. The method of claim 19, wherein the disease is acancer of the liver, uterus, cervix, bladder, kidney, colon, breast,prostate, ovary, or pancreas.